In conventional metal bellows, for example, formed metal bellows, U-shaped bellows with peaks and valleys shaped like a letter U are known (See Patent Documents 1 and 2, for example. Hereinafter they are referred to as “Conventional Art 1.”).
Also known are metal bellows characterized in that an accordion-like tube wall has peaks of a U-shaped cross-sectional shape protruding outward of the tube, and valleys of a V-shaped cross-sectional shape protruding inward of the tube (See Patent Document 3, for example. Hereinafter, they are referred to as “Conventional Art 2.”).